As has been stated in prior art patents and in industry literature, the sewing machine industry has consistently sought ways by which to increase both sewing speeds as well as the speeds with which fabrics can be handled. Higher speeds, with associated higher product output, especially in the industrial marketplace, will result in higher profits.
Traditional types of aids or sewing machine accessories, include the puller, which was invented in 1934 by Joseph Galkin and his associates, and which has been marketed since by the Joseph Galkin Corporation. Pullers have been used to overcome a natural deficiency in the way a sewing machine feed dog moves multiple layers of cloth or fabric. It is known that the feed dog will tend to push the lowest layer of cloth or fabric while the machine presser foot tends to retard the forward movement of the upper layer of cloth, with the result that the cloth must be dragged under and against the stationary presser foot. This drag causes the upper layer to slip with respect to the lower layer, with the result that a progressive loss of alignment is realized as the seam is sewn. The longer the seam, the worse this problem becomes.
Pullers are also useful in feeding heavier materials where conditions are such that top and bottom layers may slip. Various schemes have been devised to overcome the problem, such as "walking" presser feet, the substitution of a roller for the presser foot, and pulling mechanisms of the type disclosed in U.S. Pat. No. 3,960,097 granted on June 1, 1976 and entitled High Speed Gearless Fabric Puller. Other U.S. Patents that may be of interest include U.S. Pat. Nos. 2,037,088; 2,231,648; 3,083,658; and 3,141,428. The reader is also referred to British Pat. No. 528,684.
While the present invention should in no way be construed as being limited to pullers but, on the contrary, is usable in concept with any type of indexing mechanism wherein inertia problems exist, it will be helpful to the reader to set forth here some of the background of this area in the industry.
Pullers may be classified in several ways, the most important factor being whether the rollers are driven continuously by the sewing machine during the sewing operation, or intermittently in synchronism with the feed dog. Another variable is the manner in which the rollers are driven. On some rollers, only the upper roller is driven; on others the lower roller only is driven; and on superior units both rollers are used to advance the cloth or fabric. In all of these cases, the speed at which the puller can function satisfactorily is critical.
Continuously driven pullers, as opposed to synchronized pullers, have been in the past most useful on light and flexible fabrics where the fabric is able to stretch to compensate for the fact that the feed dog feeds the fabric intermittently and only when the needle is out of the fabric, while the puller is feeding the fabric continuously. Obviously, the fabric must stretch while the needle is in the cloth and the foot is not feeding. If the fabric is unable to stretch, the cloth will slip. Slipping may occur at the feed dog or at the puller rolls or, in some cases, at both places. When the cloth slips at the feed dog, the needle which is in the cloth at the time will bend and may break by rubbing against the needle plate or other machine part. Needle damage of this sort can be alleviated by increasing the presser foot pressure, and reducing pressure on the puller rolls. However, this will cause slipping to take place at the puller such that the puller will be unable to perform its functions satisfactorily.
Synchronized pullers tend to solve the problem of stretching or slipping of cloth by utilizing feed rolls that are moved intermittently in unison with the feed dog. Since the cloth is not being pulled when the needle is in it, slippage or stretching is not required. However, at relatively higher speeds, yet another problem comes into play, which concerns itself with the inherent inertia of the mechanism being utilized to handle and perform functions on the fabric.
By the term "inertia", what is referred to is the natural tendency of the actual physical mechanism employed in moving the fabric to resist both acceleration and deceleration. This problem manifests itself during attempts to cause puller feed rolls to advance intermittently every time a stitch is taken. The rollers and the rest of the associated puller mechanism must be started and stopped. This is more of a problem in the stopping of the feed rolls positively, as opposed to the starting of the rolls. When the rolls are moved at higher speeds, one experiences the consequences of Newton's law wherein the difficulty of stopping the feed rollers increases as a function of the square of the operating speed. As long as one is sewing at relatively slower speeds--for example, under 1,500 stitches per minute (spm)--conventional puller designs do not have too much trouble in stopping. However, at the upper spectrum of relatively higher operating speeds, if we double the speed one experiences the difficulty of stopping the rolls which is perhaps four times harder.
If puller feed rolls are not stopped substantially precisely at the end of each feed dog's cycle, the feed roll overshoots or, in more common parlance, turns a bit more than desired. This additional turning, while small, occurs erratically and will vary with speed and puller adjustment. The result is the undesirable varying of stitch size and slipping.
Efforts to deal with this problem have in many cases resulted in operating at speeds far below the speed capability of the sewing machine being employed. Until developments such as that disclosed within U.S. Pat. No. 3,960,097, running at relatively slower speeds was a choice chosen by most in the industry. And yet, a growing need exists for machine speeds of 6,000 to 8,500 stitches per minute, as opposed to conventional speeds of 3,500-4,000 stitches per minute.
Accordingly, it is an object of the present invention to provide an adjustable high-speed indexing system capable of use with any number of different rotating apparatus wherein inertia problems interfere with high speed indexing.
Another object of the present invention is to provide an adjustable high speed indexing system wherein, by knowing the running speed of a customer's sewing machine, appropriate parameters can be calculated so as to adjust the spring pressure certain braking means within the system.
Yet another object of the present invention is to provide a combined brake and clutch mechanism which, within an adjustable indexing system, will substantially eliminate inertial overshooting problems.
Still another object of this invention is to provide a puller attachment, or the like, which is equipped with high speed adjustable indexing means wherein a novel braking system is utilized which provides for dissipation of heat between a brake-lining member and a surrounding heat sink.
Yet another object of the present invention is to provide a puller or similar device, as above, whereby synchronized indexing is adjustable by controlling the stroke of an adjustable eccentric connecting rod, and whereby precise braked high speed intermittent pulling is accomplished.
Still another object is to provide a high speed adjustable indexing system for use with one or more types of metering devices.
Yet another object is to provide a system, as above, wherein a drum-type brake may be retrofit, or a disc-type braking arrangement may be employed, in either case facilitating speeds in excess of 6,000 stitches per minute.
The present invention fulfills the above-listed objectives, as well as many others and, in addition, overcomes the limitations and disadvantages of prior art solutions to conventional problems by providing a high speed adjustable indexing system which will hereinafter be described for and in terms of an industrial sewing machine and its associated puller attachment. The present system includes a braking arrangement which is capable of restraining either a roller equipped with a built-in clutch, or a shaft wherein the clutch is located remotely from the brake. A brake-lining member in the case of a split drum-type liner, or a pair of spaced discs in another embodiment, are caused under the adjustable biasing forces of a helical spring to produce an adjustable drag upon the rotation member against which the brake-lining is in contact. By knowing the running speed of a sewing machine, this spring pressure can be adjusted so as to provide truly synchronized high speed indexing. A predetermined area of contact between the brake liner and the surrounding structure causes a drawing off of heat produced within the brake liner member. In addition, wear, if any, is compensated for by the automatic adjustment of this same spring pressure.